Nah, all three units have large shields. Vanilla vikings don't drop like flies under missile fire unless shot in the back. My first campaign was with the Danes I remember how much my archers sucked against the rebel vikings. I thought it was because of the archers as I didn't realize how effective large shields are against missiles. It would've helped if the animation showed this, but it doesn't so you just have to imagine it.

There's no reason to build carls in the Midieval campaign. The landsmenn's advantage is that they are noble (can be trained with command stars), but so are huscarles. I would only train landsmenn if I wanted to put my early expansion into overdrive, otherwise I would wait for huscarles.